With the Iowa caucuses looming, six Republican presidential candidates clashed tonight over their conservative credentials and personal histories in a Des Moines debate that saw resurgent frontrunner Newt Gingrich battling attacks by his rivals from all sides.

But it was Mitt Romney who stole the spotlight for a $10,000 bet with Texas Gov. Rick Perry over what he wrote about the individual health insurance mandate -- then removed -- in subsequent editions of his book, "No Apologies."

"I read your first book and it said in there that your mandate in Massachusetts should be the model for the country. And I know it came out of the reprint of the book," Perry said. "But, you know, I'm just sayin', you were for individual mandates, my friend."

"I have not said, in that book, first edition or the latest edition, anything about our plan being a national model imposed on the nation," Romney said.

"I'm not in the betting business, but I'll show you the book," Perry replied.

In the first version of Romney's book, a line referring to a universal health care mandate reads: "We can accomplish the same thing for everyone in the country, and it can be done without letting government take over health care."

In the later paperback version, the line was changed to: "And it was done without the government taking over health care."

While the comparison seems to vindicate Romney, the high-dollar bet -- creating the appearance of financial excess in down economic times -- could tarnish his image, strategists said. And it immediately drew an onslaught of attacks from his rivals on both sides of the political spectrum.

"Mitt Romney probably had $10,000 in his pocket," Perry spokesman Mark Miner said after the debate.

"Mitt Romney is going to rue the day he offered a $10,000 bet in this debate," a senior Democratic strategist wrote in an email. "Talk about a window into his out-of-touch soul."

In the post-debate spin room, Romney aides said the former Massachusetts governor stands by the comment: "Romney made that bet because he knew Rick Perry wouldn't take it," strategist Eric Fehrnstrom said.

The debate, sponsored by ABC News, Yahoo! News, WOI-TV, The Des Moines Register and the Iowa Republican Party at Drake University, came just 24 days before the first GOP voters will reveal their preference for presidential nominee in caucus meetings on Jan. 3 and as Gingrich has surged ahead of Romney in several early state polls.

Romney wasted little time going after the former House speaker, accusing him of being a "career politician" with unusual -- at times liberal -- ideas.

"We can start with his idea...to have a lunar colony that would mine minerals from the moon... He said that he would like to eliminate in some cases the child labor laws so that kids could clean schools... His plan in capital gains, to remove capital gains for people at the very highest level of income," Romney said.

"But our real difference, I believe, is our backgrounds. I spent my life in the private sector," Romney said, turning to blast Gingrich as a Washington insider.

Gingrich retorted, "The only reason you didn't become a career politician is because you lost to Teddy Kennedy in 1994."

But Romney didn't back down.

"If I had been able to get in the NFL as a kid, I would have been a football star, too. But I spent my life in the private sector. We don't need folks who are lifetime Washington people to get this country out of the mess it's in -- we need people outside Washington, outside K street," he said, jabbing at Gingrich's experience.

The exchange opened the floodgates for attacks on the frontrunner Gingrich, with Rep. Ron Paul accusing him of being a flip-flopper and Rep. Michele Bachmann asserting that his office was located on "the Rodeo Drive of Washington, D.C., K Street" -- a street lined with lobbyists' offices.

But Bachmann, Paul, Perry, and former Pennsylvania Sen. Rick Santorum didn't save their fire for Gingrich alone. The contenders also hammered Romney for his shifting positions, including past support for an individual health care mandate, cap-and-trade legislation and lenient policies on illegal immigration.

Introducing a new tag line for the two top-tier candidates, Bachmann lumped them together as "Newt Romney," particularly for their mutual support of what their critics called Democratic ideas for health care reform -- charges Gingrich vehemently denied.

"I fought against 'Obamacare' every step of the way. I think it's important for you -- and this is a fair game. It's important for you to be accurate when you say those things. I did no lobbying," Gingrich told Bachmann.

But the congresswoman wasn't having it, coming back with another attack.

"This is such an important issue. We have one shot. Do we honestly believe two men who stood on this stage and defended 'Romneycare' and an individual mandate. Are they honestly going to get rid of it in 2012?" Bachmann said. "It's going to be a very heavy lift."

The debate -- the 12th for the Republican candidates this year -- comes at a crucial moment for second-tier candidates like Bachmann as they gun to knock Gingrich from the lead.

Gingrich leads the pack with 33 percent support among likely caucus goers in Iowa, according to the latest ABC News/Washington Post poll. Romney and Paul are trailing in Iowa at 18 percent each.

The former House speaker also holds impressive leads in two other key early states -- South Carolina and Florida -- with 23 percent support among likely GOP primary voters, according to the most recent CNN-Time magazine polls.

He is also positioned well in hypothetical 2012 match-ups with President Obama in swing states Florida, Ohio and Pennsylvania, new Quinnipiac University polls found.

One issue that Gingrich's rivals subtly tried to exploit during the debate was his personal history of three marriages and an admitted extra-marital affair.

Perry, who has been running ads in Iowa touting his family values and long-time marriage, took a veiled jab at Gingrich, telling the audience, "If you cheat on your wife, you'll cheat on your business partner, so I think that issue of fidelity is important."

Santorum said he believes "character" is important as an issue for voters to consider, before Gingrich was finally given the opportunity to respond.

Voters need to "have a feeling that this is a person that they can trust with the level of power we give to the presidency," he said. "I think people have to render judgment -- I've said in my case, I've made mistakes at times -- I'm also a 68-year-old grandfather and I think people have to measure what I do now."

Halfway through the debate, the spat between Romney and Gingrich flared over the issue of Israel and personal friendship with Israeli Prime Minister Benjamin Netanyahu.

Gingrich defended the controversial comments he made Friday, when he said the Palestinian people were "invented." He said tonight that his statements were "factually correct."

"Is it historically correct? Yes. Are we in a situation where every day rockets are fired into Israel while the United States -- the current administration, tries to pressure the Israelis into a peace process. Hamas does not admit the right of Israel to exist and says publicly not a single Jew will remain," Gingrich said.

"It's fundamentally time for somebody to stand up and say enough lying about the Middle East," he said.

Romney said Gingrich's comments were reckless, and that he was speaking for Israel.

"Israel does not want us to make it more difficult for them to sit down with the Palestinians. Ultimately, the Palestinians and the Israelis are gonna have to agree on how they're gonna settle the differences between them," he said. "And the United States of America should not jump ahead of Bibi Netanyahu and say something that makes it more difficult for him to do his job.

"We don't negotiate for the Israeli people," Romney said. "We stand with the Israeli people, stand with our friends, and make it very clear. We're going to tell the truth, but we're not going to throw incendiary words into a -- a place which is -- a boiling pot when our friends the Israelis would probably say, 'What in the world are you doing?'"

Gingrich retorted that he "did not speak for the people of Israel, I spoke as a historian," adding he has known Bibi Netanyahu since 1984, calling the Israeli prime minister by his nickname.

Romney countered, "I've also known Bibi for a long time," adding that they worked together at Boston Consulting Group.

"I will exercise sobriety," Romney said. "I wouldn't do anything that would alter this process. Before I do that, I get on the phone with my friend Bibi Netanyahu."

When Perry was given the chance to speak, he called the uproar over Gingrich's remarks a "minor" issue blown up by the media, channeling Gingrich's attacks on the media from other debates.

"This president is the problem, not something that Newt Gingrich said," he said.

Later, the candidates were asked about their childhood struggles and experiences through which they can identify with economically struggling Americans.

Romney admitted he "didn't grow up poor," but said his parents -- his father was the governor of Michigan, George Romney -- instilled a strong work ethic in their children because he "grew up with a dad that was poor."

Bachmann told a story she's told before, recounting her parent's divorce, which she called a "tragedy" that so many families in the country go through.

"My mom was a fulltime homemaker with four kids and we went below the poverty line overnight," mentioning that she had to start working at a young age.

"I know what it's like for single moms to struggle," Bachmann said. "We are still coupon-clippers today. ... We get what that feels like."

The very last question thrown at the candidates was what they have learned from one of their onstage rivals.

Santorum said that as a 30-year-old running for Congress -- he won his first race at 32 -- listening to Gingrich's audio tapes helped him.

Perry said it was his fellow Texan, Paul, who got him first "intrigued in the federal reserve."

"Congressman Paul is the individual on the stage that got me the most interested in a subject that I found to be quite interesting and at the root of a lot of the problems we have," Perry said.

Romney chose not to mention another candidate he learned from, but said he admired the movement that Paul has inspired, mentioning that when he goes to a debate the only signs he sees, even in the freezing cold, are Ron Paul signs.

"That enthusiasm in people, that's exciting to watch," Romney said.

Gingrich said the governor of Iowa, Terry Brandstad, who was sitting in the second row, was his role model, although not an opponent.

"Terry Branstad is my role model. Get outta politics for a while doin' something else, be involved in health care, come back when you're clearly too old, too experienced, too tied to the past, win the governorship decisively, do a great job," Gingrich said before also praising Rick Santorum "consistency and courage on Iran."

"If we do survive, it will be in part because of people like Rick who've had the courage to tell the truth about the Iranians for a long time," Gingrich said.

Bachmann mentioned a rival not on the stage: Herman Cain, who left the race last week.

"You can't have a debate without saying '999' in the debate," she said. "I think one thing that he showed us is the power of being very plain spoken."